Corrosion Resistance of Trivalent Chromium Black Passive Film on Zinc Coating

An environmental friendly trivalent chromium passivation solution without Cr6+ was prepared and a suitable sealing for the solution was choosed to study corrosion resistance of the passive film on galvanized steel sheet formed in this solution. The anti-corrosion property and morphology of the passive film were analyzed by Pb(CH3COO)2 solution spot test, tafel polarization curves, EIS and scanning electron microscopy. The results indicate that the obtained black passive film not only had an appearanced as good as that after Cr6+treatment but also complemented the problem without self-healing ability for the Cr3+ passivation. The corrosion resistance can be increased significantly after treatment with sealant.